To overcome the data-acquisition bottleneck, the use of a monolingual corpus has been explored.
A monolingual corpus can be collected relatively easily, and has been known to contribute to improved statistical machine translation [1]}.
Various attempts to employ a monolingual corpus have involved the following: pre-training of a translation model
[2]}, initialization of distributed word representation [3]}, [4]}, and construction of a pseudo-parallel corpus by back-translation [5]}.
